3 Phase Questions

[panchula]

I recently acquired a Harig 618 surface grinder. It was wired to a 3 phase supply and spun right up. I got it home, snagged a GE AF-300$ VFD from eBay. I tested the VFD with two smaller 3 phase motor I had kicking around. Both ran fine. One was 1/2 hp the other 3/4. Finally I moved the surface grinder close to it's final position, where I could access all sides. I hooked up the VFD, programmed in the amp setting and tried to start it. The motor quivered but didn't spin during the frequency ramp up over 6 seconds. I hit stop, and as the drive ramped down around 40Hz and the spindle started turning briefly. I played with shortening the ramp times, bumped up the FLA slightly with no change. It had the symptoms of a lost phase. Indeed, the VFD itself occasionally errored with an open phase warning.

I replaced the wiring between the VFD and motor. No change. I added the oil pump back into the mix, as it was originally wired. This time it spun up and as soon as it hit the operating frequency of 60HZ it errored with an over current condition. I bumped the FLA from 3.0 to 4.0 (the oil pump was rated at .5 amps). I hit run and the VFD made a "click" and died.

The motor is a Doerr 1HP, 2.8 FLA at 230V 3 phase.

Motor wiring:
T4,T5,T6 tied together. T1&T7, T2&T8, T3&T9 to UVW respectively. No shorts to ground. 2.6 ohms between the three legs and the common T4,T5,T6.
T1&T7 to T2&T8, T1&T7 to T3&T9, T2&T8 to T3&T9 all read 4ohms.

I split off all the leads and measured:
T1&T4 4.2 ohms
T2&T5 4.2 ohms
T3&T6 4.3 ohms

T7&T8 8.2 ohms
T7&T9 8.2 ohms
T8&T9 8.1 ohms

Shielded wire to motor UVW all read 0.3 ohms.

Oil pump, single phase off V&W leads reads 25.3 ohms.

All leads have infinite resistance to ground, no shorts. All readings taken with a Fluke 77 meter.

So, here's the question -- do I have a bad motor, or did I get a VFD on it's last legs?

I have a table saw I can borrow a known good VFD from, but I'd hate to smoke it. I'll definitely keep the oil pump out of the equation.



Any insights?

-Mike

[Doozer]

Maybe try unhooking the motor ground and see if that fixes it.
Could be leakage only showing up with the presence of the
background carrier frequency of the VFD.

--Doozer

[J Tiers]

The VFD, if any good, should protect itself from most problems, including a motor shorted wire-to-wire, or to ground. It sounds as if the VFD may have been an "ebay dud".

You said it "died" after a "click". What does it do now? Does it light up if there is no load on it?

If it will not light up, take your Fluke, and on ordinary ohms, with VFD disconnected from everything, read all combinations of the VFD output wires. Should be open. Read using diode range between input wires, see if it shows anything.

[macona]

You might have a ground fault issue, leakage from one of the windings to ground. Old motors can have issues some times.

First thing I would do is go into the parameters and do a factory reset, often when a VFD is tuned to a specific motor it will not work well with other motors. At least on better drives that have the tuning feature.

[wmgeorge]

Is the supply voltage single or 3 phase? If its on single phase input, VFD's are sometimes derated a lot on HP and amps.

[Sparky_NY]

I know the OP stated the motor was 230 volt but more often than not 3 phase motors are dual voltage also being able to be configured for 440-460v. Its worth double checking that the motor was not configure for 440V. I have a friend that that happen recently and its all too easy to overlook.

Other than that, I agree with others, bad VFD. Most are well protected from motor problems.

[panchula]

Dead VFD

The VFD appears to be dead. The motor was wired 230V. Has anyone used one of the Chinese meggers? https://www.amazon.com/Estone-BM500A.../dp/B00HH3ZTKE

-Mike

[J Tiers]

The VFD appears to be dead. The motor was wired 230V. ......
-Mike

So, do you mean that it does not light up at all when power is applied, even if motor is not connected?

If it does not light up, the problem is likely NOT in a part of the VFD which should get damaged by a bad motor, even in a lousy, poorly protected VFD.


Also:
For the moment, and maybe at any time, you do not need a megger, there are much easier ways of determining if you have a bad motor, at least bad enough to to credibly do damage to a VFD.

The easiest way is to connect the motor, through a switch, to 120V single phase, with a ground wire to the motor case. Insulate the 3rd wire. Wrap maybe 18" of rope on the shaft, pull start it, and when the rope has come clear off, turn it on while it is still spinning. It should run.

If you have a clamp-on ammeter, read the ground lead, which should show zero.

If it runs that way, and also runs if you connect to that third wire instead of one of the others, the motor is essentially proved good. If you want, you can use 230V instead of 120V.

[GT1]

The VFD appears to be dead. The motor was wired 230V. Has anyone used one of the Chinese meggers? https://www.amazon.com/Estone-BM500A.../dp/B00HH3ZTKE

-Mike

I have one from eBay. It appeared to work at least in the fact that it indicated the motor I had was good. My VFD indicated I had a ground fault. Turned out the fault was in the VFD itself. Prior to putting a new VFD on, I wanted to make sure the motor was not the initiator of the problem and used the megger to verify it was ok. Motor has worked great since replacing the VFD.

[wmgeorge]

I have one from eBay. It appeared to work at least in the fact that it indicated the motor I had was good. My VFD indicated I had a ground fault. Turned out the fault was in the VFD itself. Prior to putting a new VFD on, I wanted to make sure the motor was not the initiator of the problem and used the megger to verify it was ok. Motor has worked great since replacing the VFD.

What Mr. Tiers suggested is a perfect way to check a 3 phase motor, lacking 3 phase. It would be better on 230 volts but it will at least run. Clipping the ground lead to the frame will show any leakage to ground with the amp meter and bad enough will blow a fuse, our motor shop used to just put a 120 volt bulb between the frame and ground.

One of the biggest causes of VFD failure is the "Electrician" connecting the Line or power leads to the motor T output leads of the VFD.

[Mike of the North]

One of the biggest causes of VFD failure is the "Electrician" connecting the Line or power leads to the motor T output leads of the VFD.[/QUOTE]

This is how I toasted my VFD.

[wmgeorge]

Don't feel too bad, I was working in the HVAC field when I watched two electricians, who should have known better fry a 25 Hp Toshiba drive the exact same way. These guys were Union electricians and should have double checked before turning the breaker on.

[J Tiers]

It does not toast all of them. For instance, at least one model of Invertek does not get toasted that way. Yes, THAT IS indeed how I know it doesn't.

It's easy to do , particularly if the box brings the wires in closer to the "wrong" terminals than to the "right" ones. Or,as in my case, you set them on the bench that way.

[lakeside53]

And I just happen to know the Hitachi WJ200 also survives such abuse

[panchula]

All is well with the motor. I did a VFD swap from my table saw and it runs fine.

-Mike